Thus far, most clinical studies investigating the effects of inhaled corticosteroids (ICS) in asthma have concentrated on non-smoking asthmatics. However, a considerable proportion of asthma patients smokes. Cigarette smoke consists of ultra-fine particles with a diameter between 0.1 and 1 µm and therefore reaches even the smallest airways. In line with this, it has been reported that smoking is associated with small airways dysfunction. The latter may help to explain the observation that treatment with course particle inhaled corticosteroids is less effective in smokers with asthma. Recently, extra-fine particle aerosols such as hydrofluoroalkane-beclomethasone (HFA-QVAR) have become available for the treatment of asthma, which are more likely to reach the smaller airways. Based on the above, we hypothesize that extra-fine particle treatment with HFA-QVAR will be superior in improving small airways dysfunction, especially in ex-smokers and smokers with asthma.